Field of the Invention
The present invention relates to a display device and a method of driving the same, and more particularly, a display device including a touch panel and a method of driving the same.
Discussion of the Related Art
A touch panel is a type of input device that is included in display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light emitting display device (OLED), and electrophoretic displays (EPDs), and enables a user to input information by directly touching a screen with a finger, a pen or the like while looking at the screen of the display device.
A touch panel may be manufactured independently from a panel configuring a display device, and then may be attached to an upper end surface of the panel or may be provided as one body with the panel.
For example, the touch panel may be categorized into an in-cell type in which the touch panel is built into a pixel of the panel displaying an image, an on-cell type in which the touch panel is provided on the panel, and an add-on type in which the touch panel is manufactured independently from the panel and then is attached to an upper end of the panel.
An in-cell type touch panel may be more aesthetic and slimmer, and thus application of the in-cell type touch panel has expanded. That is, the demand for an in-cell type display device, in which elements configuring a touch panel are built into a panel to reduce the thickness of portable terminals such as smart phones and tablet personal computers (PCs), is increasing.
FIG. 1 is an exemplary diagram for describing a related art method of driving a touch panel, and FIG. 2 is an exemplary diagram for describing a related art method of sensing a touch in a touch panel.
A touch panel senses a user's touch, and may be implemented in various types such as a resistive type and a capacitive type. Hereinafter, a touch panel using the capacitive type will be described with reference to FIG. 1.
A below-described touch panel 10 is an in-cell type touch panel, and is supplied with a driving voltage. The touch panel 10 includes a plurality of driving electrodes TX, which are formed in parallel with a plurality of gate lines formed in a panel into which the touch panel 10 is built, and a plurality of receiving electrodes RX which transfer a plurality of sensing signals, generated by the driving voltage, to a touch sensing unit. The touch sensing unit includes a driver, which supplies the driving voltage to the driving electrodes TX, and a receiver which determines whether there is a touch, by using the sensing signals received from the receiving electrodes.
In a related art display device including the touch panel 10, in order to determine whether the touch panel 10 is touched, the driving voltage is sequentially supplied to the driving electrodes TX, and the sensing signals are received from all the receiving electrodes RX while the driving voltage is applied to the driving electrodes TX.
The sensing signal corresponds to a capacitance which is generated between the driving electrode TX and the receiving electrode RX by the driving voltage, and the touch sensing unit analyzes an amount of change in the capacitance to determine whether the touch panel 10 is touched.
In an in-cell type display device, the driving electrodes TX and the receiving electrodes RX perform a function of a common electrode which is formed in a pixel formed in the panel and is supplied with a common voltage.
Therefore, during an image display period, the driving electrode TX and the receiving electrode RX perform the function of the common electrode which receives the common voltage supplied to the pixel. Also, during a touch sensing period, the touch sensing unit supplies the driving voltage to the driving electrode TX, and determines whether the touch panel is touched, by using the sensing signal received from the receiving electrode.
For example, in order to drive the related art in-cell type display device, a period (hereinafter simply referred to as one frame period) corresponding to one frame is divided into the image display period and the touch sensing period.
During the image display period, the common voltage is supplied to the driving electrodes TX and the receiving electrodes RX. During the touch sensing period, a pulse-type driving voltage is supplied to the driving electrodes TX, and the sensing signals are transferred from the receiving electrodes RX to the touch sensing unit.
In the touch panel applied to the in-cell type display device, the driving electrodes TX and the receiving electrodes RX are formed on the same plane, where a distance between adjacent electrodes may be short, and the electrodes are formed in the pixel. Therefore, a capacitance generated between the driving electrodes TX and the receiving electrodes RX may be large.
A display device including the touch panel 10 may be applied to small electronic devices such as smartphones, tablet personal computers (PCs), notebook computers, monitors, etc. Therefore, parasitic capacitance may not greatly affect the sensing performance for small electronic devices.
However, the touch panel 10 may be applied to large display devices such as large televisions (TVs), large monitors, and electronic bulletin boards. In this case, the number of parasitic capacitors exponentially increases, and thus, the parasitic capacitance increases. When the parasitic capacitance increases, a load of the receiving electrode RX increases, and for this reason, a sensing performance of the touch sensing unit is degraded. That is, when the related art in-cell type touch panel is applied to a large display device having a large area as-is, the load of the receiving electrode RX increases due to the parasitic capacitance, and for this reason, the sensing performance of the touch sensing unit is degraded.
Moreover, in the related art in-cell type touch panel using a differential driving method, a first driving voltage and a second driving voltage are respectively supplied to two adjacent driving electrodes TX, and then whether one of the two driving electrodes TX is touched is determined by comparing a plurality of sensing signals received from the receiving electrodes RX. For example, as illustrated in FIGS. 1 and 2, when four driving electrodes TX1 to TX4 are formed in the touch panel 10 in parallel with the gate lines, during a first touch sensing period, the touch sensing unit supplies the first driving voltage to a first driving electrode TX1, supplies the second driving voltage to a second driving electrode TX2, and analyzes levels of the sensing signals received from the receiving electrodes RX to determine whether the first driving electrode TX1 is touched. Also, during a third touch sensing period, the touch sensing unit supplies the first driving voltage to a third driving electrode TX3, supplies the second driving voltage to a fourth driving electrode TX4, and analyzes levels of the sensing signals received from the receiving electrodes RX to determine whether the third driving electrode TX3 is touched. However, when a lowermost driving electrode TX4 which is formed at a lowermost portion of the touch panel among the driving electrodes TX is touched, there is no driving electrode TX which is compared with the lowermost driving electrode TX4. Therefore, in order to determine whether the lowermost driving electrode TX4 is touched, as illustrated in FIG. 2, a sensing signal generated from the second driving voltage which is applied to an additional driving electrode TXa which is not formed in a display area of the touch panel is used, a sensing signal generated from the second driving voltage which is applied to an uppermost driving electrode TX1 which is formed at a position opposite to the lowermost driving electrode TX4 is used, or an arbitrary sensing signal is used. Therefore, whether the lowermost driving electrode TX4 is touched may be inaccurately determined.